When an electrical signal travels along a medium it gets attenuated depending upon the medium characteristics. That is why a LAN cannot send signal beyond a certain limit imposed by the different types of LAN technologies. To increase the length of the LAN, repeaters are frequently used. Repeaters in its simplest form relay analog electric signal. It means that they transmit the physical layer signals or data and therefore correspond to the bottom layer of OSI model.

Repeater amplifies the signal, which has got attenuated during the course of transmission because of the physical conditions imposed by the transmission media. It also restores the signal to its original shape. The specific characteristic of repeater is that whatever it receives it transmits to the other LAN segment. This does not understand the frame format and also physical addresses. In other words, it is a transparent device. Therefore, multiple LANs connected by repeaters may be considered as a single LAN.

Generally, the maximum size of an Ethernet is considered to be 500 meters. When two Ethernet with maximum size segments are connected together using repeater will make the total length to 1000meters.In the same manner two repeaters connect three segments together and transmit signal from one end to another. That is, signal can travel up to 3000 meters. Is it possible to extend the length of LAN in this manner up to any arbitrary length? The answer is no. Ethernet follows CSMA/CD access mechanism for successful transmissions of signal which is based on low delay. By extending the length of Ethernet beyond certain limit will greatly hamper delay time of CSMA/CD mechanism.

It is shown that maximum four repeaters are used to extend Ethernet segments into a single Ethernet network. However, connection between two segments can be extended over a long distance by using fiber modems. This is, known as Fiber Optic Intra Repeater Link (FOIRL).

The main disadvantage associated with repeaters is their transparent nature because the signal received at one segment is truly transmitted to the other segment. Repeater does not understand the language of frame and therefore, cannot distinguish between noise and signal. When a collision occurs on one segment, the same along with noise produced by collision is reproduced on the other segment by repeater.

Classification of Repeaters

Repeaters can be classified into two categories. These are local and remote repeaters. Local repeaters are used to connect LAN segments separated by a very small distance.

Remote repeaters are used to connect LAN segments that are far from each other. A transmission line known as a link segment is provided between two remote repeaters. No nodes can be connected to this line.